1. Field of the Invention
The present invention relates to a mobile communication system, and more particularly, to a method of determining the data rate of traffic data to be transmitted from a mobile station to a base station, in which a delay time is considered when assigning the reverse data rate.
2. Discussion of the Related Art
In a contemporary mobile communication system, data is transmitted from a mobile station to a base station using a reverse traffic channel, and a reverse control channel is used to transmit control information corresponding to the traffic data. The control information includes data rate information and mobile station status information, e.g., the currently available traffic channel transmission power and the currently remaining buffer capacity, as well as other data necessary for controlling the data transmission of the traffic channel. This control information is transmitted as a signaling message via the reverse link of a traffic channel and is used in determining, based on the data rate of a previous frame of the reverse link, a data rate for subsequent traffic data. That is, based on previous transmission information, the mobile station transmits to the base station a request for assignment of a data rate, i.e., a change to or the maintenance of the current transmission rate, receives a response from the base station in the form of data rate control information, namely, a rate control bit or RCB, and determines the transmission rate of the next frame based on the received data rate control information.
As described above, a delay time exists between the mobile station's request for a particular data rate and its subsequent transmission of data at that rate. This delay time can be seen in FIG. 1, illustrating a reverse-link data rate determination method according to a related art. During an ith frame, a mobile station transmits control information on the reverse control channel (RCCH) and transmits traffic data on the reverse traffic channel (RTCH). Responding to the control information of frame i, the base station transmits data rate control information on the forward control channel (FCCH) at an (i+α)th frame. The next frame to which the mobile station may apply the data rate control information is an (i+β)th frame, which reflects an overall delay time of β frames. The assigned date rate of the frame i+β, however, is calculated with respect to its immediately preceding frame—that is, an assigned date rate is applied to the rate of the (i+(β−1))th frame—and the mobile station determines the optimal data rate for the transmitting frame accordingly. In doing so, the mobile station calculates an assigned data rate for each frame based on the data rate control information transmitted from the base station, to achieve a maximum transmittable data rate according to a current communication environment.
In the above method of determining a reverse data rate according to a related art, the assigned data rate is a value equal to εi+αDi+(β−1) for every frame i+β, where εi+α is a data rate transition ratio determined in accordance with the data rate control information of the (i+α)th frame and where Di+(β−1) is the transmitted data rate of the (i+(β−1))th frame. Accordingly, as indicated by the arcing arrow in FIG. 1, the transmitted data rate of the (i+(β−1))th frame is referenced to determine the assigned data rate of the (i+β)th frame.
FIG. 2 illustrates a case where the RCB from the base station permits a data rate increase of the reverse traffic channel after transmitting a hold for frames i+1 and i+2. In this example, when the RCB indicates an increase in the transmission rate for frames i+3, i+4, and i+5 and the data rate transition ratio is equal to 2, the assigned data rates for each frame is a doubling of the immediately preceding frame, i.e., frame i+(β−1). Here, the data rate is initially assumed to be a unity value (d=1).
Though the method of the related art considers the current communication environment, there is no provision for the delay time required for the generation and transfer of data rate control information, during which the communication environment is apt to change, and an error is generated as a result. Such an error prevents the base station from fully utilizing a scheduling algorithm for the application of the resource distribution to each mobile station.